The use of wire mesh is ubiquitous. Some examples of its uses include forming barriers, fences (including security fences), cages (including cages to contain animals, while keeping other animals and people out) and so on.
Wire mesh is typically formed by interlacing strands of wire, called pickets. The pickets are shaped to form a desired pattern for the mesh. A common pattern is the diamond pattern which is formed by interlacing a pair of pickets where each picket is formed in a zig-zag configuration. An end of the mesh is generally formed by cutting each picket after it leaves the pattern at the edge of the mesh. The cut off section is generally known as a picket tail. The picket tails are usually sharp and protrude from the edge of the mesh. This not only creates a safety issue, but also provides little impediment to the edge of the mesh being unravelled. Therefore, there is always a need to finish off the edge with an edge finishing.
A common method of edge finishing in the past involved twisting the two picket tails at the end of the interlaced pickets as shown in FIG. 1. While this can be effective in maintaining the integrity of the mesh at the edge, it still creates a significant safety concern as the twisted ends are both rigid and sharp. This method of edge finishing is no longer allowed to be used for some applications in some countries.
Another method of the prior art consists of bending each of the picket tails around each other and back onto the picket to from a single knuckle finishing, as illustrated in FIG. 2. While safer than the twisted finishing, the single knuckle joint can lack the strength to maintain the integrity of the mesh at the edge, and can be pulled apart if sufficient force is applied (for example by being pushed by a large animal).
Of particular interest to the present invention is the use of wire mesh to form a cage for aquaculture. Increasingly in many parts of the world mesh is used to contain fish while they grow. The mesh is typically formed from specially treated wire to increase the lifetime of the mesh in an aquatic environment, and to limit or prevent build up of aquatic matter on the mesh (thus reducing the frequency of cleaning the mesh). These mesh cages, which can extend to the bottom of the water (ocean, river or lake for example) typically have a circumference of around 130 m. The mesh cages need to be sufficiently strong and rigid to both keep the farmed fish safely inside and to keep predator fish out.
The edge finishing of a mesh cage for aquaculture therefore needs to have sufficient strength to maintain the integrity of the mesh around the perimeter against the weight of the mesh, and be safe to handle. The knuckle finishing of FIG. 2 can be too weak for this purpose, while the twisted finishing of FIG. 1 can be too dangerous to handle.
One solution proposed to solve these issues is a double knuckle arrangement as shown in FIG. 3. This arrangement involves bending a pair of pickets at an intersection on the edge of the mesh into a U-shape with its open end facing back towards the body of the mesh, the U-shape lying in the same plane as the mesh. The finishing may be completed by bending the picket tail around an adjacent picket to form a knuckle. When this is done for each pair of pickets (and picket tails) the result, as shown in FIG. 3 is known as a double knuckle since each loop includes two knuckles. The double knuckle edging may be safer than the twisted finishing, but it can still be a hazard if anything catches on the exposed picket tails.
Furthermore, this arrangement can have the disadvantage that the configuration of adjoining U-shaped loops and the manner in which the final knuckles are formed can make forming this double knuckle by machine very difficult. This form of double knuckle is typically formed manually which can have a number of disadvantages, including a significant increase in the labour, time and cost of producing a mesh with this type of double knuckle finishing. Furthermore, as the knuckles are formed manually there can be irregularities in the knuckles around the edge of the mesh, which can lead to distortion of the mesh and uneven distribution of the load on the edges of the mesh which can result in high wear/failure of the over loaded edge.
However a more significant issue is that the length of the preformed picket (i.e. the distance between bends in the picket) and the length of the picket end can be insufficient to completely double back over the adjacent picket when completing the first bend and to form the knuckle. This can result in the adjacent picket being pulled closer to the folded picket, opening a gap between them, as illustrated in FIG. 3. This gap is locked in when the knuckle is completed. Testing has indicated that each gap can be at least 2 mm and in many instances up to 8 mm. The cumulative affect of all the gaps around the circumference (˜130 m) of the edge can amount to a shortening of the edge of at least 11 meters in comparison to the central portion of the mesh. A major issue that is caused by a shortened edge is that additional pickets are required to meet a given specification for a length of mesh. Additional pickets for a given length of mesh increases the manufacturing cost and also increases the per meter weight of the mesh, requiring additional floats to be provided for mesh fish cages. Shortening of the edge can also result in a loss of tension in the central portion of the mesh, which in turn can lead to increased rubbing of the pickets at each intersection, thus increasing wear, and removing any surface preparation of the wires (for example antifouling treatment). Furthermore, the loss of tension can create a situation where a large predator can charge at the un-tensioned section of the mesh and can stun or kill the fish inside.
As mentioned earlier it should be appreciated that the applications of the present invention are many and varied so the discussion in relation to aquaculture is just an exemplary example to aid understanding.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.